Rail heads and impedance bonds


Rail heads are parts of rail current circuit, mounted next to the track. Heads are used for immediate powering of isolated sections from one end, and for returning the power from the other end of track circuit into the relay room to the receiver (track relay). Heads consists of: housing, cover, stand, cable glands with protective pipe, resistor or condenser with damper and connector.

On electrified tracks are used:

  • BsSk 1727/141 simple power head
  • BsSk 1727/142 double power head
  • BsSk 1727/143 simple relay head
  • BsSk 1727/144 double relay head
  • BsSk 1727/146 relay head
  • BsSk 1727/147 power rail head


Impedance bond is used on electrified tracks to separate return line of traction current from the power for rail current of track circuit. Impedance bond has double function: it enables galvanic continuity through isolated structure for return traction current and disables current flow from one section to the next section. According to the way of use, it can be power or relay bond. On the power side, an impedance bond transforms the power from the power transformer to voltage needed for powering of track circuit. On the relay side, at the end of the section, it transforms track power to the value needed for attracting control relay. It is placed into concrete housing next to the rails, directly by isolated rail structure.


  • Nominal input voltage – 1V
  • Nominal frequency of track circuit – 83 1/3 Hz
  • Input impedance of joint impedance bond – 140-160 mΩ
  • Weight of impedance bond – 65 kg
  • Dimensions – 550×290×270 mm